Heretofore, an electrical junction box for a vehicle has been known which includes a power distribution circuit for distributing a power source for a vehicle to a plurality of vehicle-mounted loads, and a control circuit for controlling an on-off action of switching elements (for example, a relay switch, and a transistor) included in the power distribution circuit.
For example, an electrical junction box disclosed in Patent Document 1 includes a wiring board for constituting the power distribution circuit, and an ECU board for controlling an on-off action of a semiconductor relay packed on the wiring board. The ECU board includes a board body, and a plurality of L-shaped terminals projecting downward from the board body. When these L-shaped terminals are connected to suitable positions on a power distribution unit, the power distribution circuit formed on the wiring board and the control circuit on the ECU board are electrically interconnected.
In the electrical junction box, since the semiconductor relay having a relatively great calorific value is packed on a wiring board side while the control circuit that is weak in a relatively high temperature is incorporated in an ECU board side, it is possible to restrain the control circuit from being subject to a heat adverse effect due to a heat generated from the semiconductor relay.
However, the electrical junction box disclosed in Patent Document 1 involves the following problems to be overcome.
a. It is difficult to reduce a difference in area between the wiring board that constitutes the power distribution circuit and the ECU board that constitutes the control circuit. This difference in area will interfere with downsizing of the whole of the electrical junction box. In general, as shown in FIGS. 2 and 3 in Patent Document 1, since the wiring board that constitutes the power distribution circuit must widen a width of a wiring pattern in order to comply with a great current, the area of the wiring board becomes greater than that of the ECU board mounting only the circuit board. This difference in area will become great as the power distribution circuit becomes complicated. It will be difficult to effectively contain both boards in a single casing assembly as the difference in area becomes great. In result, it will become difficult in downsizing of the casing assembly.
b. A number of terminals are required for interconnecting the power distribution circuit on the wiring board and the control circuit on the ECU board. In addition, the number of the terminals will increase as the switching elements included in the power distribution circuit increase. Such increase of the number of the terminals will invite upsizing of a connector including the terminals, thereby interfering with enhancement of reliability in connection. Patent Document JP 2007-228757 A